1. Field of the Invention
This invention concerns methods and arrangements for non-invasively detecting the systolic and diastolic blood pressure values, and more particularly such methods and arrangements adapted to automated determinations of such blood pressure values.
2. Description of the Prior Art
The measurement of systolic and diastolic blood pressure values in human subject for clinical and diagnostic purposes has traditionally been carried out by a doctor, nurse or other clinical technician by a procedure including inflating an occluding cuff encircling the subject's upper arm to a pressure value corresponding to that in which blood flow in the arm is occluded. The pressure in the cuff is then allowed to decline gradually to a pressure value in which blood flow can take place substantially unimpeded by the cuff. The doctor or nurse listens by means of a stethoscope for certain sounds known as the Korotkoff sounds created by the initiation of blood flow in the arterial vessels, which sounds occur characteristically at cuff pressure values corresponding to systolic and diastolic blood pressure values. By observing a manometer which monitors cuff pressures, the examiner can thus determine systolic and diastolic blood pressure values. The systolic blood pressure value is that value existing within the blood circulatory system as the point of maximum heart contraction while the diastolic blood pressure value is that blood pressure existing in the circulatory system when the heart is in its relaxed or uncontracted condition. Due to the pervasive incidence of abnormalities in blood pressure, the insidious onset of such condition, and the potentially highly destructive effects on the individuals afflicted, it has heretofore been seen as highly desirable that mass screening of potential victims be continually carried out. Such mass screening would preferably involve an automation of the blood presure measurement process to reduce the need for involvement of highly trained medical personnel.
Such automation would also be advantageous within hospitals and other medical facilities to reduce the cost of operation by minimizing the extent of services required by such highly trained individuals while it saved time providing adequate diagnostic support for such operations. Obviously, reliable and accurate results would be essential from any such apparatus. Numerous such atuomated systems have been proposed and implemented in the past, one such system being described in co-pending application ser. No. 714,097, filed on Aug. 13, 1976, entitled METHOD AND ARRANGEMENT FOR MEASURING BLOOD PRESSURE. In this system the blood pressure wave form which is the variation of pressure with time in the cuff as the cuff is cycled through an occluding-non-occluding cycle is analysed with certain characteristic changes in the wave form being established as criteria for detecting the systolic and diastolic pressure points. Other methods have involved the use of a microphone and other means for automatically detecting the presence of the so-called Korotkoff sounds.
Another approach involves the use of plethysmography to detect the blood flow conditions in the extremity downstream of the cuff with the existence of a flow or no-flow condition used to identify the systolic and diastolic pressure values.
Yet another approach involves tonometry in which a force transducer is used to directly measure the pressure existing in the arterial network directly without the need of an occluding cuff, and the maximum and minimum pressure values detected which correspond precisely to systolic and diastolic pressure values.
All these approaches are theoretically valid but each suffer from various disadvantages.
Firstly, the pressure values so obtained should correspond very closely to values which would be obtained by the exercise of traditional procedures since the body of clinical data which exists and provides a reference for forming diagnoses had been obtained by the use of these traditional procedures. For a number of reasons no automated measurement technique has heretofore provided such close correspondence.
Secondly, these techniques all involve rather sophisticated apparatus and electronic processing equipment, i.e., micro-processers or mini-computers and analyses of rather complex electronic variables, such that the results of such analyses is not highly reliable and repeatable, leading to a certain distrust of the results of such tests carried out on such apparatus. This attributes in no small part to a widespread reluctance to rely on such apparatus by the doctors and nurses responsible for such examinations.
Further, such apparatus commonly use sensitive transducers, microphones, etc. which are apt to require extensive and regular skilled maintenance, and which tend to malfunction, particularly when subject to abuse which would be the case if such apparatus was installed in public buildings, etc. for coin operated applications.
These factors, while contributing to a degree of a lack of reliability, also tends to increase the expense of manufacturing and operating such equipment.
Accordingly, it is an object of the present invention to provide a method or technique of making blood pressure measurements corresponding to the systolic and diastolic pressure values which is adapted to such automated measurements and which is inherently highly reliable.
It is another object of the present invention to provide such a method and apparatus which produces readings which closely correspond with readings taken by the traditional clinical procedures.
It is yet another object of the present invention to provide such an apparatus which is relatively simple and troublefree and requires little maintenance while at the same time producing highly repeatable results.